Confused about how PEOs like JustWorks manage their "Master Policy" insurance

I'm considering joining a small company that uses JustWorks which offers an Aetna "Master Policy." At first I was under the impression that this is a policy that pools everyone in different companies together, so you get a large group rate, so all these small companies get a relatively stable offering.

But on some of their pages, they say your company's rate is determined by its usage. Are they just talking generally, or am I misunderstanding the concept of a "Master Policy"? Or do they create their own rates internally based on what they see companies using?

They offer plans to companies with as few as 2 people, so I don't see how that would work out as 'insurance' unless they're pooled onto some larger plan.

I have an autoimmune disease and expensive insurance, so I worry about being 'noticed' in a small company thanks to potentially increased costs.

submitted by /u/Albedo100
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